Diagnoses

Microbiology

Epidemiology

Spread of infection to a contiguous joint

In children younger than 2 years of age the common blood supply of the metaphysis and epiphysis crosses the physis and can allow spread of a metaphyseal abscess into the epiphysis and eventually into the joint. The hip joint is the most commonly affected in young patients; however, the physes of the proximal humerus, radial neck, and distal fibula also are intraarticular, and infection in these areas can lead to septic arthritis as well. In severe infection, epiphyseal separation can occur in children younger than 2 years of age.

In older children this common circulation is no longer present and septic arthritis is rare.

After the physes are closed, infection can extend directly from the metaphysis into the epiphysis and involve the joint. Therefore septic arthritis due to acute hematogenous osteomyelitis generally is seen only in infants and adults.

The age distribution of acute hematogenous osteomyelitis in children is bimodal, generally affecting children younger than 2 years of age and those between the ages of 8 and 12 years.

Preponderance in males is observed in all age groups. Factors related to increased incidence in males may include increased trauma due to risk-taking behavior or other physical activities that predispose to bone injury.

Causative organisms may be summarized by patient group, as follows:

Children younger than 1 year: Group B Streptococcus species, Staphylococcus aureus, Haemophilus influenza (5-50%), and Escherichia coli

Children older than 1 year: S. aureus, E. coli, H. influenza, Serratia marcescens, and Pseudomonas aeruginosa

Adults: S. aureus, E. coli, S. marcescens, and P. aeruginosa

Individuals with sickle cell anemia and trait: Salmonella species and S. aureus

Individuals with diabetes: Gram-positive cocci, such as Streptococcus, Staphylococcus, and Enterobacter species

The evaluation of acute hematogenous osteomyelitis should begin with a history and physical examination. Signs and symptoms can vary significantly.

Fever, bone pain, swelling, redness, and guarding the affected body part are common. Long bones, including the femur, tibia, and humerus, are most commonly affected.

Inability to support weight and asymmetric movement of extremities are often early signs in newborns and young infants.

Often, patients are able to localize the infected bone on examination, owing to pain. Symptoms include focal swelling with cardinal signs of inflammation with or without fever and focal point tenderness over the affected bone. It is important to note whether the adjacent joint is involved by assessing the range of motion of the joint and signs of inflammation. Arthritis found on examination may be a reactive inflammatory response or a sign of an infected joint.

In infants, the elderly, or immunocompromised patients, clinical findings may be minimal. Fever and malaise may or may not be present in the early stages of the disease, although pain and local tenderness are common findings. Swelling may be significant, and compartment syndrome has been reported in children.

The white blood cell (WBC) count often is normal, but the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level usually are elevated.

The CRP is a measurement of the acute phase response and is especially useful in monitoring the course of treatment of acute osteomyelitis because it normalizes much sooner than the ESR.

The causative organism can be identified in approximately 50% of patients through blood cultures.

Imaging Studies

* Plain roentgenograms generally are negative but may show soft tissue swelling. Skeletal changes, such as periosteal reaction or bony destruction, generally are not seen on plain films until 10 to 15 days into the infection.

But in differential diagnosis the radiography can be useful in revealing bone tumors, fractures, and healing fractures.

* Technetium-99m bone scintigraphy (three-phase technetium radionuclide bone scanning) can confirm the diagnosis as early as 24 to 48 hours after onset in 90% to 95% of patients. Gallium scans and indium 111—labeled leukocyte scans also can aid in diagnosis when used in conjunction with technetium scanning. A 3-phase bone scan with technetium 99m is probably the initial imaging modality of choice.

* Magnetic resonance imaging (MRI) can show early inflammatory changes in bone marrow and soft tissue.

* Ultrasonography may demonstrate changes as early as 1-2 days after onset of symptoms. Abnormalities include soft tissue abscess or fluid collection and periosteal elevation. But this modality is difficult to use in acute cases of osteomyelitis, with limitations based on availability, technician-dependent results, and an inability to differentiate fluid patterns as infectious versus traumatic.

Procedures

If signs and symptoms do not begin to resolve within 48-72 hours of initiation of appropriate antimicrobial treatment, consider bone aspiration to drain the pus.

Bone aspiration usually gives an accurate bacteriological diagnosis and should be performed with a 16- or 18-gauge needle in the area of maximal swelling and tenderness, usually the long bone metaphysis. The subperiosteal space should be aspirated first by inserting the needle to the level of the outer cortex. If no purulent material or fluid is encountered, the needle is placed through the cortex to obtain a marrow aspirate.

CT or ultrasound-assisted aspiration is indicated in suspected hip or vertebral osteomyelitis.

Дата добавления: 2014-10-15